The primary component of conventional broadloom carpet products such as carpet tiles is tufted “greige” carpet. Greige carpet generally comprises fiber tufts looped around a primary backing fabric. Primary backing fabrics may be woven, nonwoven, or spun bonded natural or synthetic materials. The tufted loops of fiber may be left intact or sheared so that the upright face fibers, or pile, are left with random ends facing outwards on the visible wear surface, or face side, of the carpet.
In order to more permanently secure the fiber tufts looped around the primary backing fabric and provide dimensional stability to the finished product, secondary backing materials may be applied to the back side of the greige carpet.
Common secondary backing materials include latex, urethanes, thermal plastics such as PVC, and modified olefin-based thermal formable plastics. Additionally, woven materials such as oriented polypropylene, polyesters, jute, and other nonwoven felted type materials may be used as secondary backing materials. A variety of additives intended to impart other desirable characteristics to the finished carpet, including resistance to fuzzing (individual fibers pulling loose during usage), moisture impermeability, fire retardency, sound absorbency, and antibacterial properties also may be added as secondary backing materials.
Secondary backing materials may be secured to the greige carpet using, for example, a hot melt adhesive. Additionally, hot melt adhesives may perform other beneficial functions when applied to greige carpet. For example, if the hot melt adhesive is able to penetrate into the fiber tufts during application, then the adhesive may help secure the fiber tufts to the primary backing material and prevent fuzzing. Also, hot melt adhesives may impart additional mechanical strength to the greige carpet.
For example, U.S. Pat. No. 6,503,595, the disclosure of which is incorporated herein by reference in its entirety, discloses a carpet that includes a primary backing having tufts of synthetic carpet fibers protruding from a top surface and, optionally, a secondary backing with an extruded sheet of a polyolefin polymer between the primary and secondary backing. The polyolefin sheet adheres to the primary and secondary backings, thereby fusing the two together.
In order to facilitate the penetration of the hot melt adhesive into the tufted fiber bundles of the greige carpet, it may be desirable to chose an adhesive that has a low viscosity but at a relatively low temperature. However, such an adhesive often does not have adequate mechanical strength to impart dimensional stability to the greige carpet. Conversely, mechanically stronger adhesives often attain low viscosity only at higher temperatures, necessitating application of the adhesive at higher temperatures. Higher process temperatures may cause the greige carpet to shrink and may damage the primary backing material and fiber tufts, resulting in a loss of finished carpet and increased manufacturing costs. The dichotomy between low viscosity and low application temperature sometimes makes application of hot melt adhesives difficult.
Several methods have been utilized in an attempt to overcome the difficulties associated with applying hot melt adhesives to greige carpet and secondary backing materials.
For example, in order to avoid higher process temperatures and associated damage to the greige carpet, hot melt adhesives with higher viscosities (and therefore greater mechanical strength) may be applied to a greige carpet and pressed into the fiber tufts by means of high pressures. For example, the greige carpet may be coated with a hot melt adhesive that is heated but only to a temperature sufficiently low to avoid damaging the greige carpet. The hot melt adhesive coated greige carpet then is nipped at high pressure. Nipping at pressures, however, may result in distortion of the carpet because of the flattening of the fiber tufts at the face side of the carpet.
For example, U.S. Pat. App. No. 2002/0193474, the disclosure of which is incorporated herein by reference in its entirety, discloses a modified hot melt adhesive which is applied in an extruded form. The hot melt backing is nipped under high pressure against a cool roller, thereby flattening and cooling the yarn loops.
Additionally, U.S. Pat. No. 4,576,665, the disclosure of which is incorporated herein by reference in its entirety, provides a hot melt adhesive bonded pile fabric that comprises a liquid permeable base layer and a pile forming yarn adjacent to the base layer but not tufted through the base layer, the pile forming element having been bonded to the base layer by means of a hot melt adhesive applied to the back of the base layer. The hot melt adhesive applied to the back of the base layer is forced through the permeable base layer using an applicator roll to apply pressure.
Alternatively, U.S. Pat. No. 3,962,012, the disclosure of which is incorporated herein by reference in its entirety, teaches a process for laminating a primary and a secondary sheet that seeks to avoid damaging the face side of the primary sheet by applying an adhesive to the back side of the primary sheet or to the mating side of the secondary sheet, or to both, contacting the mating side of the secondary sheet with the back side of the primary sheet, and firmly pressing together the two sheets while avoiding the application of any pressure to the pressure-sensitive face side of the primary sheet until at least 50 percent of the terminal bond strength is developed. The two sheets are firmly pressed together by maintaining the primary and secondary sheets taut and applying pressure from the back side of the secondary sheet.
Instead of the use of pressure, the hot melt adhesives may be applied at higher temperatures so that the adhesive is less viscous. This may be accomplished, for example, using heated lamination rolls. However, heated lamination rolls are often sullied by loose fibers that adhere to the roll, therefore necessitating shut down for cleaning.
In another alternative, multi-layered hot melt adhesives may be utilized. One of the layers is typically a low-melting point adhesive that easily infiltrates the fiber tufts attached to the primary backing material. The other layer is typically a high-melting point adhesive that imparts additional mechanical strength to the greige carpet. Forming a multi-layered hot melt adhesive, however, may introduce additional complexity and cost into the manufacturing process.
For example, WO 2004/025018, the disclosure of which is incorporated herein by reference in its entirety, describes a process for marrying a secondary backing material with an unfinished tufted primary carpet using a hot melt adhesive. The hot melt adhesive comprises two adhesive layers applied by contiguous extrusion—a lower viscosity layer to lock the fibers in place and a higher viscosity layer to thicken and flatten the entire adhesive coating. The lower viscosity layer of hot melt adhesive is intended to be pressed into and around the fiber roots.
Another method to apply hot melt adhesives is to pre-form an adhesive layer before applying the adhesive layer to the greige carpet and secondary backing material. Again, pre-forming an adhesive layer may introduce additional complexity and cost in the manufacturing process.
For example, U.S. Pat. No. 6,479,125, the disclosure of which is incorporated herein by reference in its entirety, teaches the production of a finished carpet employing a multitude of layers. A heated film of thermofusible bonding material with a lower melting point than that of the primary carpet and backing materials is used to encapsulate the layers without excessively heating the fibers or layers themselves. However, the film must be preformed in order to have consistent weight distribution across the carpet.
U.S. Pat. No. 4,844,765, the disclosure of which is incorporated herein by reference in its entirety, teaches the lamination of a tufted primary carpet into a finished product with the use of hot melt adhesive in sheet form. The sheet of hot melt adhesives is preformed and subsequently laminated between the unfinished primary tufted carpet and the secondary backing while at an elevated temperature.
Several other patents teach other methods to produce finished broadloom carpet using hot melt adhesives. For example, U.S. App. No. 2003/0211280, the disclosure of which is incorporated herein by reference in its entirety, provides a method of making a carpet comprising a greige carpet and an adhesive backing material. The adhesive backing material is applied to the greige carpet by extrusion coating and at least one additional step selected from (a) preheating the greige good prior to the application of the adhesive backing material, (b) subjecting the adhesive backing material to a vacuum to draw the adhesive backing material onto the back side of the primary backing material, (c) subjecting the adhesive backing material to a positive air pressure device in addition to nip roll pressure to force the adhesive backing material onto the back side of the primary backing material, and (d) heat soaking the carpet after application of the adhesive backing material onto the back side of the primary backing material.
The description herein of problems and disadvantages of known apparatus, methods, and compositions is not intended to limit the invention to the exclusion of these known entities. Indeed, embodiments may include one or more of the known apparatus, methods, and compositions without suffering from the disadvantages and problems noted herein.